For the first time ever on Friday morning, the National Hurricane Center issued a Tropical Storm Watch for parts of Southern California, as Hurricane Hilary rapidly intensified to Category 4 strength. Hilary is likely going to be a high-impact event for the northern Baja California peninsula as well as the southwestern United States.

As of 12:00 a.m. MDT (2:00 p.m. EDT) Friday, Hurricane Hilary was centered near 18.2°N 111.8°W, and was moving northwestward at approximately 10 mph. Maximum sustained winds were 125 knots (145 mph), with an estimated minimum pressure of 939 mb. This makes Hilary the most intense hurricane of the 2023 Pacific season so far, and the strongest hurricane by minimum pressure in the basin since Barbara in 2019. Hilary may be peaking in intensity, as it appears as if the satellite appearance has degraded slightly since early this morning, and there are signs of a double eyewall structure. Regardless, Hilary remains a very intense hurricane and interests in the Baja California Peninsula and the southwestern United States should be prepared.

Although some slight additional intensification cannot be ruled out later today, Hilary is expected to turn more to the north-northwest tonight. In about 24-36 hours or so, Hilary will begin moving over significantly cooler waters, which should cause a faster weakening trend. Regardless, all of the models show Hilary maintaining deep convection as the center moves into southern California, so it appears likely we will see a very rare bonafide tropical cyclone impact for the southwestern United States. Hilary is likely to still be a hurricane as the center nears the coast of the central and northern Baja California peninsula. Hilary is expected to produce rainfall amounts of 2-4″ along the Baja and southern California coasts, with higher rain totals inland. While these totals may not seem like much, it is a lot for a region that does not typically experience tropical cyclones. A Hurricane Warning is currently in effect for the Baja California peninsula from Punta Abreojos to Punta Eugenia. A Hurricane Watch is currently in effect for the Baja California peninsula north of Punta Eugenia to Ensenada. A Tropical Storm Warning is currently in effect for the Baja California peninsula from Punta Abreojos southward, as well as from from Loreto southward. A Tropical Storm Watch is currently in effect for the Baja California peninsula north of Loreto, mainland Mexico north of Huatabampito, Baja California north of Ensenada to the California/Mexico border, from the California/Mexico border to the Orange/Los Angeles County Line, and Catalina Island.

There are currently four systems being monitored in the Atlantic for possible tropical development, with two of the four being potential land threats. Three of the disturbances are currently in the Atlantic’s Main Development Region (MDR), and have formed as a result of a monsoon trough breakdown.

The easternmost system, Invest 98L, is a broad area of low pressure located over the eastern tropical Atlantic. As of 12:00 UTC Friday, Invest 98L was centered near 15.5°N 32.9°W. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1009 mb. The National Hurricane Center (NHC) currently gives 98L a 60 percent chance of development within 48 hours, and a 70 percent chance within 7 days. 98L remains broad, and global models suggest it may struggle to develop a more compact circulation. Environmental conditions are only marginally favorable for development of 98L, with sea surface temperatures of near 27°C (80.6°F). In addition, wind shear is expected to increase significantly in about 48 hours or so, and some Saharan dust will make sustained convection development difficult. It does not appear likely that 98L will be more than a weak tropical storm at most, and 98L is not expected to threaten land.

The next system, Invest 99L, is located over the central tropical Atlantic. As of 12:00 UTC Friday, Invest 99L was centered near 13.3°N 44.0°W. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1009 mb. The NHC currently gives 99L a 40 percent chance of development, both within 48 hours and 7 days. 99L could still develop into a short-lived tropical depression, but global model support for this system has been decreasing and upper-level winds are expected to become less conducive to development. 99L does not appear likely to threaten land.

The westernmost system along the monsoon trough, which is yet to be given an Invest designation, is the most likely of the three MDR disturbances to threaten land. The NHC currently gives this system a 10 percent chance of development within 48 hours, and a 30 percent chance within 7 days. A more distinct area of low pressure is likely to form east of the Lesser Antilles tomorrow or Sunday. Global models such as the ECMWF and GFS have been trending stronger with this system potentially developing over the eastern Caribbean Sea. Although development in the Caribbean Sea is rare during El Nino events, vertical wind shear has actually been below average in the eastern Caribbean thus far in the 2023 Atlantic hurricane season.

Last but not least, an area of disturbed weather is currently producing disorganized showers and thunderstorms north of Hispaniola. This area of disturbed weather is expected to track westward into the Gulf of Mexico in a few days, where a broad area of low pressure is likely to form. Thereafter, gradual development into a tropical cyclone is possible. Although global models are not currently very enthusiastic with this system, it is worth noting that previous systems in this region (like Hurricanes Hanna and Sally in 2020) were poorly forecast by computer models. With the potential threat to Texas or northern Mexico, this disturbance needs to be monitored for potential development.